Heat sensitive transfer sheet having screen layer and method of making



July 29, 1969 D. A. NEWMAN HEAT SENSITIVE TRANSFER SHEET HAVING SCREENLAYER AND METHOD OF MAKING Flled Feb 14 1967 INVENTOR. qyl 14A/M7700 6fa@ \\v United States Patent 3,458,335 HEAT SENSITIVE TRANSFER SHEETHAVING SCREEN LAYER AND METHOD OF MAKING Douglas A. Newman, Glen Cove,N.Y., assignor to Columbia Ribbon and Carbon Manufacturing Co., Inc.,Glen Cove, N.Y., a corporation of New York Filed Feb. 14, 1967, Ser. No.616,025 Int. Cl. B41m I/24; B44d 1/22 U.S. Cl. 117-15 8 Claims ABSTRACTF THE DISCLOSURE There are several known systems forthermographicallyproducing copies of infrared radiation-absorbing imagesusing a transfer layer which liberates image-forming vapors in theheated areas, corresponding to the location of the original images, toform duplicate copies of the original. The vapor images may betransferred rst to the original sheet, such as over the original images,and then transferred to one or a succession of copy sheets in a secondheating step, or may be transferred directly to the copy sheet in asingle operation to make a single copy or a master copy sheet such as aplanographic printing plate. U.S. Patents Nos. 3,121,650 and 3,262,386are illustrative of such processes and the colored and colorformingvaporizable or sublimable materials useful therein.

In a related copying process, illustrated by British Patent No. 943,401,the image-forming vapors consists of oil which is deposited on the copysheet in the heated image areas to form latent images which may bedeveloped by contact with a thermoplastic powdered ink which adheres tothe copy sheet only over the oily latent images and which can be setthereon by heating to render the ink tacky and to cause it to bond tothe copy sheet surface. In cases where the copy sheet is a planographicplate, the oily images are oleophilic and the plate is suitable for usesince the images become developed with color in the planographicprinting process.

While these processes produce fair results, they have the disadvantagethat the vapor donor layer is either wet, as is the case with oils, oris relatively unstable so that the vaporizable or sublirnable materialtransfers or leaches to the sheet in contact therewith on storage so asto provide overall staining of the second sheet after a relatively shorttime and prior to use. It is not possible to avoid this diiculty bymeans of a conventional supercoating over the donor layer since thisseals the layer and prevents escape of the vapors in the heated areas.

Some prior processes and materials of this type have the addeddisadvantage that the vaporizable imaging material is trapped to a largeextent in a binder material in the donor coating and is unable tovolatilize and escape and form the duplicate images. Only that portionat or near the surface of the donor layer is available for imagingpurposes and the remainder is wasted within the donor layer, so that theformed images are weaker in intensity than is desired. To avoid thisdifficulty, the image-forming material is often used as a pureimpregnation or surface coating on the donor sheet, free of bindermaterial, and

lice' this is generally undesirable since much is lost within thefoundation and escapes through the uncoated surface during the heatingoperation.

It is the principal object of the present invention to provide a vapordonor sheet which may be stored in contact with an original sheet or acopy sheet for prolonged periods of time without straining the originalor copy sheet.

It is an object of one embodiment of this invention to provide a vaporydonor -sheet which contains a large source of vaporizable imagingmaterial which is substantially completely available for imagingpurposes free 0f masking binder materials.

These and other objects and advantages of this invention will be obviousto one skilled in the art in the light of the present disclosureincluding the drawings in which:

FIGURE 1 is a perspective view of a vapor donor sheet according to thepresent invention.

FIGS. 2 and 3 are perspective views 0f a continuous foundation webcarrying a donor coating and being printed thereover with differenttypes of open screen layers.

FIG. 4 is a diagrammatic cross-section, to an enlarged scale, of animaged original sheet, a vapor donor sheet and a copy sheet superposedunder the influence of infrared radiation but spaced for purposes ofillustration.

The present invention involves the discovery that the provision of anopen line screen layer over a coating or impregnation of heatvaporizable or sublimable material prevents the transfer of the materialto sheets in contact therewith, even over prolonged contact duringstorage, without interfering with the ability of the material totransfer freely under the effects of applied heat. This discovery isquite surprising in view of the migratory nature of vaporizable andsublimable materials to materials in contact therewith and appears to bedue, at least in part, to the fact that the applied open screen consistsof a synthetic thermoplastic resinous or plastic composition which isincompatible with and a non-solvent for the vaporizable or sublimableimage-forming material.

Aside from the presence of the open screen layer, the donor sheets andcopy sheets and image-forming materials of the present invention may beidentical to those known in the art as exemplified by the aforementionedpatents. However, according to the preferred embodiment the donor layercontaining the image-forming material has a formulation and structurewhich is novel in this field and which provides for the inclusion oflarge amounts of image-forming material in a form which is more readilyand more completely releasable under the effects of applied heat.

Donor sheets 10 according to one embodiment of this invention are shownin the drawings and comprise a flexible foundation 11 such as paper orplastic iilm, a donor layer l2 containing an image-forming materialwhich is releasable as a gas under the effects of applied heat, and anopen screen layer 13 over the donor layer and consisting of intersectingstrips which form a multiplicity of openings 14 through which thegaseous image-forming material can escape during the heating operation.

Suitable donor layers are those which consist of the image-formingmaterial coated onto the foundation or impregnated therein in the caseof absorbent foundations such as paper, or layers containing a suitableheat-resistant binder material such as a synthetic thermoplastic resinor plastic material. According to the preferred embodiment, theimage-forming material is present as a solution or dispersion in an oilcontained within a porous structure of a synthetic thermoplastic resinwith which the oil is incompatible or insoluble. Structures of this typeare well known in the carbon paper iield, as illustrated by U.S.

Patents Nos. 2,820,717; 2,944,037; 3,037,879 and 3,117,- 018, and theformulations taught by said patents are useful according to thisinvention provided that the present image-forming materials aresubstituted for the pigments and dyestuls of the patents. The amount ofimage-forming material may be increased as much as desired and the donorsheet is re-usable since the image-forming material circulates throughthe porous resin structure so that heated portions of the donor layerare continuously supplied with fresh imaging material particularly incases where the latter is dissolved in its oily vehicle.

The open screen layers suitable for use according to the presentinvention may have several different forms and structures. The preferredstructure is that shown in FIG. 1 of the drawings in which the screenconsists of intersecting strips to form discrete openings. Such a screenis preferably applied as shown in FIG. 2 by means of an offset printingtechnique. A thin layer of a solution of the synthetic thermoplasticfilm-forming composition is supplied from a solution fountain (notshown) to applicator roll using a doctor blade (not shown) to controlthe thickness. The applicator roll transfers a thin layer of thesolution to the peaks of a printing cylinder 16 containing raised lineareas or peaks 17 and discrete valleys 18 which receive no ink. Thedonor sheet 10 is expended from supply roll 40 and is passed in the nipbetween the printing cylinder 16 and an impression roll 41 whereby thedonor layer 12 is overprinted with screen layer 13. The printed web isthen heated to evaporate the solvent and dry the screen layer prior tothe rolling of the final web on take-up roll 42.

According to another embodiment illustrated by FIG. 3, the open screenlayer may have a gravure structure which is a negative of the structureshown in FIG. 2 in that the screen has open intersecting line areas 22which surround spaced islands or spots 23 of the synthetic thermoplasticfilm-forming composition. Such a structure is formed in the manner shownin FIG. 1 whereby the printing cylinder 16 is coated with a solution ofthe film-forming composition by immersion in a solution fountain (notshown) and a doctor blade (not shown) is used to scrape the solutionfrom the peaks 17 of the cylinder so that only the discrete valleys 18of the cylinder contain a supply of the solution. The solution isprinted over the donor layer and dried to form a screen of the typeshown.

It should also be pointed out that it is not necessary that the openscreen layers of the present invention have a square configurationconsisting of intersecting printed or unprinted areas as shown in FIGS.2 and 3. The printing cylinder may have its raised area or peaks in theform of closely spaced parallel lines running in only one direction andforming between them hollow depressions or valleys which are alsoparallel and uninterrupted. Such screens may also be applied accordingto the techniques of either FIG. 2 or FIG. 3.

The synthetic thermoplastic film-forming composition for the screen ispreferably a solution of a resin or plastic in a volatile organicsolvent which is a non-solvent for the binder of the donor layer if oneis present. Also the resin or plastic of the screen layer isincompatible with and a nonsolvent for the imaging material of the donorlayer.

Preferred resins for the screen layer are vinyl resins such as vinylchloride-vinyl acetate copolymer, acrylic resins such as polymethylmethacrylate, polystyrene, cellulose plastics such as cellulose acetate,cellulose nitrate, ethyl cellulose, and the like.

The open screen layer need not have a straight or square configurationas shown in the drawings. The printed areas may be curved or zig-zag ormay intersect each other at any desired angle. The only requirement isthat the screen consists of printed areas which are at least 0.00001inch and not more than 0.01 inch in height or thickness and thatparallel strips or spots be spaced from each other by at least 0.00001inch and not more than about 0.01 inch. Preferably the strips are from0.0001 inch to about 0.001

. 4 inch in height and thickness and are spaced by at least 0.0001 inchand no more than about 0.05 inch.

The following examples are given by way of illustration and should notbe considered as limitative.

Example 1 A donor sheet was prepared by coating a paper web with thefollowing composition to form a donor layer having a thickness of 0.001inch after evaporation of the solvents.

Ingredients: Parts by weight, gm.

Vinyl chloride-vinyl acetate copolymer (Vinylite VYHH 10.0

Mineral oil 5.0

Butyl stearate 5.0

Du Pont Oil Orange 0.1

Ethyl acetate 50.0

Toluol 10.0

Ingredients: Parts by weight, gm. Ethyl cellulose 10 Ethyl alcohol 40Bronze powder '2 After evaporation of the solvent, the open screen layernearly completely masks the underlying donor layer from view, -dueprimarily to the presence of the bronze powder, but actually contains anumber of openings through which the Oil Orange vapors can pass underthe effects of heat. The ethyl cellulose screen consists of intersectingstrips which are about 0.0001 inch in height and width and which arespaced by 0.001 inch.

In carrying out the copying process, the donor sheet 10 is superimposedwith an imaged original sheet 20 and a copy sheet 30 in the order shownby FIG. 4 and infrared radiation is applied to the original sheet suchas by lamps 50. The radiation is selectively absorbed byradiation-absorbing images 21 and converted to heat of at least C. whichis conducted to the donor sheet as an image pattern. The heated areas ofthe donor layer give ot vapors of the Oil Orange which stain contactingportions of the copy sheet to form an exact duplicate of the original.The images formed on the copy sheet appear continuous and no sign of theetect of the intervening screen layer is visible to the naked eye.

Example 2 A donor sheet was prepared by coating a web of 0.5 milpolyethylene terephthalate polyester lm (Mylar) with a 5% solution ofrubeanic acid dissolved in methyl ethyl ketone and, if desired, 2% byweight of a soluble binder such as polyvinyl butyral. After evapation ofthe solvent a thin donor layer of about 0.001 inch thickness remains. y

Next a white-colored open screen layer is printed over the donor layerin the manner shown in FIGURE 1 using the following composition for thescreen layer.

Ingredients: Parts by weight, gm. Polyvinyl acetate l0 Titanium dioxide2. Butyl acetate 40 The copy sheets adapted for direct imaging by meansof the donor sheets of this example are prepared by coating sheets ofpaper on one surface with an aqueous solution containing 15% by weightnickelous acetate and 50% by weight urea and dissolving the water toleave hydrated nickelous acetate and urea deposited on or near the papersurface in an amount equal to about 4% by weight of the paper.

The copying process was effected by superimposing the sheets in theorder shown in FIG. 4 of the drawing, the coated surface of the copysheet being in contact with the open screen layer of the donor sheet andapplying infrared radiation to heat the original images to at least 150C. and cause the rubeanic acid to sublime in the heated image andtransfer to the copy sheet as an image pattern and react with the nickelions to form a deep blue nickel-dithioxamide complete reaction productin the form of images corresponding to the images 0n the original sheet.The urea functions as a catalyst or flux for the reaction.

In cases where it is desired to employ a vaporizable oily material asthe imaging material for the formation of latent images to be developedby contact with dry pigment, the procedure of Example 1 may be followedwith the exception that the Oil Orange is omitted from the donorcomposition and the mineral oil and butyl stearate are replaced withparts by weight of a lightbodied mineral oil having a boiling point ofabout 330 C. A longer exposure is generally required to insure adequateheat build-up in the image.

After the transfer of the mineral oil vapors to the copy sheet, the oilyimages are contacted with a powdered mixture of equal parts by weight ofcarbon black and a resin binder such as colophony resin. The powderadheres only to the oily latent images and is shaken from the remainderof the sheet. Then the sheet is heated by the infrared radiation sourceagain to fuse the resin powder in place and form the duplicate copy ofthe original.

The printing cylinders useful according to the present invention arecommercially-available engraved rolls having fine linear peaks at therate of from about 50 to about 200 per inch, the depressions between thepeaks being from about 0.00001 inch to about 0.01 inch in depth.

Finally it should be understood that the phrase copy sheet is usedherein and in the amended claims to include sheets developed as finalcopies and also sheets imaged for use as masters or planographicprinting plates.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. A thermographic transfer sheet which absorbs substantially noinfrared radiation and which comprises a flexible foundation sheetcarrying a uniform distribution of imaging material which is vaporizablefrom one surface thereof under the effects of heat, and having printedover said surface a multiplicity of uniform, parallel, nontransferablestrips of synthetic thermoplastic resin which is incompatible with saidimaging material, said strips being between 0.00001 inch and 0.01 inchin height and thickness and being uniformly spaced from each other bybetween 0.00001 inch and 0.01 inch in distance, the spaces between saidstrips permitting the unimpeded free transfer of said imaging material,in vapor form, to a copy sheet to form images thereon which appearsubstantially unbroken to the naked eye, said strips spacing saidimaging material from a copy sheet in contact with said strips toprevent contact-migration of said imaging material to said copy sheet inunheated areas.

2. A transfer sheet according to claim 1 in which said imaging materialcomprises a layer positioned on the surface of the foundation sheet.

3. A transfer sheet according to claim 2 in which said layer comprises aporous structure of nlm-forming binder material having said imagingmaterial dispersed in the pores thereof.

4. A transfer sheet according to claim 1 in which said strips arebetween about 0.001 inch and 0.0001 inch in height and thickness and arespaced from parallel strips by from about 0.05 to 0.0001 inch.

5. The process of producing a thermographic transfer sheet which absorbssubstantially no infrared radiation which comprises the steps of (a)applying a uniform distribution of a heat-Vaporizable imaging materialto a exible foundation sheet.

(b) printing over said imaging material a multiplicity of uniform,parallel strips comprising a volatile solvent solution of a syntheticthermoplastic resin which is incompatible with said imaging material,and

(c) evaporating said volatile solvent to produce dried strips which arenon-transferable and which are from 0.00001 inch to 0.01 inch in heightand thickness and which are uniformly spaced from each other by from0.00001 inch to 0.01 inch in distance, the spaces between said stripspermitting the unimpeded free transfer of said imaging material, invapor form, to a copy sheet to form images thereon which appear unbrokento the naked eye, said strips spacing said imaging material from a copysheet in contact with said strips to prevent contact migration of saidimaging material to said copy sheet in unheated areas.

6. The process according to claim 5 in which the imaging material ispresent within the pores of a porous layer of film-forming bindingmaterial.

7. The process according to claim 5 in which said strips are betweenabout 0.001 inch and 0.0001 inch in height and thickness and are spacedfrom parallel strips by from about 0.05 to 0.0001 inch.

8. In the process for producing copies of original infraredradiation-absorbing images in which said images are superposed with atransfer sheet carrying an imaging layer comprising heat-Vaporizableimaging material and infrared radiation is applied to heat the originalimages and cause the imaging material in corresponding portions of saidlayer to vaporize and deposit on a copy sheet in the form of imagescorresponding to said original images, the improvement which comprisesusing as the transfer sheet one having an open ne screen layer over thetransfer layer in order to space the transfer layer from the copy sheetand prevent contact-migration of the imaging material to unintendedareas of the copy sheet, said screen layer comprising a multiplicity ofuniform, parallel, non-transferable strips of synthetic thermoplasticresin which is incompatible with said imaging material, said stripsbeing between 0.00001 inch and 0.01 inch in height and thickness andbeing uniformly spaced from each other by between 0.00001 inch and 0.01inch in distance, the spaces between said strips permitting theunimpeded free transfer of said imaging material, in vapor form, to thecopy sheet so that the images formed on the copy sheet appearsubstantially unbroken to the naked eye.

References Cited UNITED STATES PATENTS 1,962,082 6/1934 Miller 117-3642,313,645 9/1940 Antrim 117-364 2,790,742 4/ 1957 Wharton 117-3642,803,579 8/1957 Stolle et al 117-36.4 3,080,954 3/1963 Newman et al117-364 3,104,980 9/ 1963 Maierson 117-4364 3,121,650 2/1964 Meissner117-362 3,260,612 7/1966 Dulmage et al 117-36.2 3,262,386 7/ 1966 Gordon117-362 MURRAY KATZ, Primary Examiner U.S. Cl. X.R.

PO-Ofo UNTED STATES RATENT OFFICE @emmene cow-Recueil Patent No.31,458,335 Dated July Z9, 1969 Inventor(s) Douglas A. Newman lt iscertified that: error appears in the above-dentifie'd'patent and thatsaid Letters Patent; are hereby corrected as shown below:

- Column I?, line 7, "straining" should read staining;

Column )4, line M3, "superimposedn should read superposed line 65,"FIGURE l" should read Example l Column 5, line E, "superimposlngg"should reed superposing line ll*a after "image' insert areas line 13,"complete" should read complex line 26, "image" should reed images linegl, "amended" should read appended Column 6, line 9, the period shouldread under' References Cited, No."2,313,645" should read 2,213,6u5

SIGNED ND SEALED MAR 24.1970

(SEAL) Attest:

Edward M. Fletcher, Ir,

Attesting Officer WILLIAM E. SGHUYIER, JR.

Commissioner of Patents

